Power line carrier system



March 3, 1936'. E. GREEN 2,032,360I

POWER LINE CARRIER SYSTEM Filed Deo. l2, 1930 23- 5* 8 L 'Cla-rent Masal'l'n 3 m 6 Astra/elias .Mm Zmzs mission Zine 1- o o'o M fw 2 @params n." v

ATTORNEY Patented Mar. 3, l 19.3.6

UNITED STATES accesso PATENT oFFlcE American Tele one and Telegraph Company,

, a corporation of New York .Application December 12, 1930, Serial No. 501,985 4 claims. v (c1. 1rzc5z) i 'I'his invention relates to transmission of sig- ",nals at carrier frequencies over power lines, and

particularly to means for terminating the power line's at high frequencies.

5 Aspointed out in the copendng application of Aifel and Green, Serial No. 501,984, iiled December 12, 1930, a power line circuit is less well adapted for carrier communication than the or-'.

diriaryv telephone circuit, owing to the presence of apparatus upon the powerline whose impedance may be low for the range of frequencies employed in carrier transmission. Because of circuit derived from a power line are extremely erratic .was a function of frequency. In the said copendng application there is described a network for terminating a power line at carrier frequencies, which network is designed to have the characteristic impedance of the line throughout the range of `carrier frequencies employed. The arrangement thereinA shown is conductive- 1y bridged across the circuit to be terminated. The present invention resides in a network for terminating a power line at high frequencies, which network isieifectively connected with the system by utilizing a portion of the apparatus normally employed in the power system-namely, the current transformers that are connected with the powerline for the purpose o f measuring the magnitudes 'of the power currents flowing thereover.

This invention will be understood from the following description when read in connection with 3'5 the attached drawing, of which Figure 1 shows schematically a network to terminate completely a three-phase transmission line at 'carrier fre- "quencies, and Fig. 2 shows a modincation of cthe invention for use' in terminating a single phase o carrier circuit derived from a three-phase power line. In Fig. 1, I, 2 and 3 represent the conductors of a three-phase spurrline L, which is connected with the main transmission line at the point X.'

50 and 3 at or near the station where the power,-

apparatus 4 is llocated are the currrent transformers T1, Tz and Ts', having their primary windings connectedin series with the said conductors. lIhese transformers forni part of the 55 apparatus normally employed at a power station quencies.

for the measurement of the currents flowing over the transmissionrlines. The secondary winding of -transformer T1 is 'connected with a current measuring instrument A1, and in like manner the corresponding windings of Atransformers T2 5 and T: are connected with the instruments Az and Aa. Such instruments would normally be connected in series with the said secondary windings and -ground to indicate the magnitudes of the currents flowing over the conductors of the lo line L. Since those current transformers have windings of relatively fewl turns, the distributedl capacity is quite small, and consequently, they are quite effective transformers at carrier frequencies, In view of that fact,`it is possible to 15 employ those' transformers to effectively connect with the said' line the terminating network Ato terminate the said line at the carrier fre- This is accomplished by using a high pass filter structure with shunt termination. It 20 will be seen' that the left-hand terminals/of the secondary windings of transformers T1, T2 and T3 are connected to ground by conductor 5, and that the current measuring instruments A1, A2 and Aa 'are connected to ground by the conductors 6, 'I 25 and 8, respectively. Bridged across the conductors 5 and 8 are the inductances, 9 and I0, between which is connectedthe condenser I I In similar manner, the inductances I2 and I3 andv condenser I4 are connected between conductors 30 5 and 1; and likewise, inductances I5 and I6 and condenser I1 are` connected between coni ductors 5 and G; The resistance I8 is shunted across inductance I0, resistance I9 across inductance I3, and resistance 20 across inductance 35` I6. Condensers 2|, 22 and 23 shunt the current measuring instruments A1, A2 and A3, respectively, for the carrier frequencies.

The impedance networks. 24, 25 and 26, that are connected in series with conductors I, 2 and 40 3, respectively, of the spur line, serve to render the impedance high at carrier frequencies of that portion of the spur line looking toward the power apparatus. The combination of the terminating networks and the impedancenetworks, as shown in 'th'e spur line, provides a smooth termination of that line at carrier frequencies and thus elim; inates an impedance irregularity in the system.

I'he use of the current transformers represents an economical arrangement for associating the terminating net-work with the'said line. In the design or calibration of the current transformers, allowance can be made for the presence of such inductance as is included in series with them.

.Iny addition to being of value in connection resonance` action when the line is 10 with power'line' carrier systems, the terminating arrangement of Fig. 1 may bef advantageously lemployed in reducing the en'ect upon a power `system of transient currents that result from short circuits, lightning, etc. Since the arrangement effectively terminates the line in an impedance approximating its characteristic impedance, it prevents the building up of high potentials by shocked by transients, lightning, etc.

- Fig, 42, in which the same reference numerals have been employ as in Fig. 1 toindicate similar parts, shows the applicationof the invention for'terminating one phase of a three-phase translthe condenser 32, and as the other pillar the inductance .33, a terminating resistance 34 being shunted across the inductance 33. Such a networkmay be designed to give a constant impedance of suitable value atall frequencies above the critical frequency of the iilter, while the inductance aiords free passage to the power currents. In view of the description of the invention disclosed in Fig. 1, further explanation of Fig. 2

seems unnecessary. Y

While the invention has been disclosed ed in certain forms, it is to be undeA toodthat such showing is purely schematic, and that the invention is not ,limited except as defined byv the appended claims.

- Whatisclaimedis:

1. 4In a system for the transmission of power currents, a multi-phase transmission line, each conductor of said line having connected in-serie`s therewith the primary winding of a current transformer, the secondary windings of said current transformers lbeing connected to current measuring devices, a multi-phase wave filter connected in circuit with said measuring devices, saidV dwave filter being terminated in resistances, and

the arrangement' and proportioning .of said current transformers,current measuring devices` wave filter and terminating resistances being such as to present a low impedance for the frequency of said power currents. and being such as to terminate said transmission line at carrier fre-v quencies in an impedance approximately equal to its characteristic impedance. j

2. In a system forl the transmission of powerA currents, a multi-phase transmission line, each conductor of said line having connected in series therewith the primary winding of a current transformer, all secondary windings of said current transformers having one terminal connected to a common conductor,- an inductance connected "line at frequencies substantially .frequency of vsaid power, currents.

in series with a current measuring device bctween said common conductor and the other terminal of each current transformer, each of said current measuring devices being shunted by a condenser, said inductances forming partl of a 5 multi-phase wave filter, said wave filter being terminated inv resistances, the combination of said current transformers, current measuring devices, wave filter and terminating resistances presenting a low impedance to said power cur- 10 rents and being so proportioned as to terminate saidtransmission line at canier frequencies Ain p former, each .ofsaid current measuring devices 25 being shunted by a condenser, said4 inductances v 'forming partA of a multi-phase wave lter, said f wave filter being terminated in resistances, the Y impedance presented by saidwave iiltery at carrier frequencies being approximately equal to the 3o characteristic impedance vof said transmission line divided by the-impedance 'transformation ratio of said current" transformers. 4. In a system f orthe transmission of power* currents, a multi-,phase transmission line, each 3'5 conductor of said line having connected in se ries therewith the primary winding of arcurrent rtransformer, all secondary windings `oi said vcurrent transformers having one terminal connected Y to a common conductor, an inductance connect- 40 ed in series with'a currentmeasuring device beY tween said common conductor and the other ter` minal of the secondary winding of each current transformer, each of ysaid current-measuring de vices being shunted bya condenser, each ofthe u saidinductances being.' shunted/by-*a condenser in seriesrwith another inductance and each 6i" said other inductances being shunted by a resistance. the said inductances and intermediate condensers` being -so proportioned as to form a 50 multi-phase wave filter capable of passing frequencies substantially higher than the frequency l of said power currents. the impedance introduced in said transmission line by the l combination of 'current transformers, current measuring de- 58' Ipower currents and being substantially equalto the characteristic impedance of said transmission higher the 60 ns'rru. Lamu. 

